Road curvature estimation for rearview mirror adjustment system

ABSTRACT

A system and method for automatically correcting the viewing angle of a rear-view mirror on a vehicle when the vehicle is traveling around a curve. The system estimates the curvature of the road using only vehicle speed and vehicle steering angle information. The road curvature estimation is used to determine the radius of curvature of the road, which can then be used to determine the corrected viewing angle of the rear-view mirror. Depending on whether the road is curving to the right or to the left will determine whether the left side rear-view mirror or the right side rear-view mirror will be adjusted.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a system and method for adjusting the rear-view mirrors of a vehicle and, more particularly, to a system and method for automatically adjusting the rear-view mirrors of a vehicle based on the curvature of the road on which the vehicle is traveling, where the curvature of the road is determined using only vehicle speed and steering angle.

2. Description of the Related Art

The automotive industry makes considerable effort to improve the safety of vehicles and their occupants. One of the areas of concern has been the limited field-of-view provided by the rear-view mirrors of the vehicle.

Rear-view mirrors of a vehicle are oriented to provide the driver of the vehicle with an optimum rear viewing zone behind and towards the left and towards the right of the vehicle. For manually adjustable rear-view mirrors, the rear viewing zone is a fixed region of space in the vicinity of the vehicle, which is at a particular orientation relative to the vehicle. The orientation of the rear viewing zone can be adjusted by adjusting the rear-view mirrors.

When the vehicle is traveling on the road, where the profile of the road is changing, a fixed rear viewing zone may limit the view of the driver and may lead to accidents involving pedestrians, bicycle riders and other vehicles not seen by the driver because of the fixed rear viewing zone. In such cases there is a need to correct the rear viewing zone of the mirror to get a desired view.

The problem of a limited rear viewing zone becomes even more prominent in the case of vehicles towing a trailer, tractor-trailers, articulated buses and the like as the line of sight is further limited due to the bending of the vehicle combination.

One existing system that addresses the above-mentioned problem for vehicles towing trailers determines the change in distance between the vehicle and the trailer to identify that the vehicle is making a turn, and adjusts the rear-view mirror accordingly to optimize the rear viewing zone. The system makes use of magnetic field sensors mounted on the vehicle and the trailer. However, the use of magnetic sensors leads to problems because there are a number of electrical devices in a vehicle that may affect the functioning of such magnetic sensors. Further, this system can only be used for vehicles towing a trailer.

Another existing system provides an automatic adjustment of rear-view mirrors based on the turning of the vehicle around a vertical axis. However, this system does not adjust the rear-view mirrors when the vehicle is moving downhill or uphill.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a system and method are disclosed for automatically adjusting the viewing angle of a rear-view mirror on a vehicle when the vehicle is traveling around a curve. The system estimates the curvature of the road using only vehicle speed and vehicle steering angle information. The road curvature estimation is used to determine the radius of curvature of the road, which can then be used to determine a corrected viewing angle of the rear-view mirror. Depending on whether the road is curving to the right or to the left will determine whether the left side rear-view mirror or the right side rear-view mirror is adjusted.

Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a vehicle traveling around a curve showing a corrected viewing angle of a right side rear-view mirror of the vehicle;

FIG. 2 is an illustration of a vehicle traveling over a hill showing a corrected viewing angle of the side rear-view mirrors of the vehicle;

FIG. 3 is an illustration of a vehicle traveling up a hill showing a corrected viewing angle of the side rear-view mirrors of the vehicle;

FIG. 4 is an illustration of a vehicle towing a trailer around a curve showing a corrected viewing angle of the right side rear-view mirror of the vehicle;

FIG. 5 is a block diagram of a system that corrects the viewing angle of a rear-view mirror of a vehicle, according to an embodiment of the present invention;

FIG. 6 is an illustration of a vehicle traveling around a curve depicting the turning radius of the vehicle;

FIG. 7 is an illustration of a vehicle traveling around a curve showing various variables that are used to determine the corrected viewing angle of a side rear-view mirror of the vehicle;

FIG. 8 is an illustration of a vehicle traveling over a hill showing variables that are used to determine a corrected viewing angle of the rear-view mirrors of the vehicle;

FIG. 9 is an illustration of a vehicle towing a trailer around a curve showing variables that are used to determine a corrected viewing angle of the ride side rear-view mirror of the vehicle; and

FIG. 10 is an illustration of a vehicle towing a trailer showing the trailer in a straight orientation and an angled orientation, and defining triangles that are used to calculate a corrected viewing angle for a rear-view mirror on the vehicle when the trailer dimensions are known.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the invention directed to a system and method for automatically changing the viewing angle of a rear-view mirror of a vehicle in response to road curvature is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses.

FIG. 1 is an illustration of a vehicle 10 traveling around a curve 12 in a road 14. The vehicle 10 includes a left side rear-view mirror 16 and a right side rear-view mirror 18. The left side rear-view mirror 16 includes a normal rear viewing zone 20 and the right side rear-view mirror 18 includes a normal rear viewing zone 22. The rear viewing zones 20 and 22 are set by the vehicle driver for his size and seat position so that the driver is able to see the most optimum rear viewing zone when the vehicle is traveling straight. Because it is not reasonable for the driver to make adjustments to the rear-view mirrors 16 and 18 while he or she is driving, the rear viewing zones 20 and 22 will not be optimum when the vehicle 10 is traveling around the curve 12. Particularly, when the rear-view mirror 18 is in its normal viewing position, a vehicle 24 traveling along an inside lane of the road 14 around the curve 12 may not be seen by the driver using the normal rear viewing zone 22. Therefore, the present invention proposes a technique, as will be discussed in detail below, for automatically correcting the viewing angle of the rear-view mirror 18 a proper amount based on the degree of curvature of the curve 12 to provide a corrected rear viewing zone 26 so that the vehicle 24, and possibly other vehicles and objects, will be visible to the driver of the vehicle 10.

FIG. 2 is an illustration of the vehicle 10 traveling down a hill 32 where the normal rear viewing zones 20 and 22 of the rear-view mirrors 16 and 18 will be directed upward because of the slope of the hill 32 so that objects, such as vehicle 34, may not be in the rear viewing zones 20 and 22. As will be discussed in detail below, the present invention proposes automatically changing the viewing angle of the rear-view mirrors 16 and 18 a proper amount based on the slope of the hill 32 to provide a corrected rear viewing zone 36 were the vehicle 34 will be visible to the driver of the vehicle 10.

FIG. 3 is an illustration of the vehicle 10 traveling up a hill 40 where the normal rear viewing zones 20 and 22 of the rear-view mirrors 16 and 18 will be directed downward because of the slope of the hill 40 so that objects, such as vehicle 42, may not be in the rear viewing zones 20 and 22. Therefore, as will be discussed in detail below, the present invention proposes automatically changing the viewing angle of the rear-view mirrors 16 and 18 a proper amount based on the slope of the hill 40 to provide a corrected rear viewing zone 44 were the vehicle 42 will be visible to the driver of the vehicle 10.

The present invention also proposes automatically changing the rear viewing zone of the rear-view mirrors 16 and 18 if the vehicle 10 is towing a trailer around a curve. FIG. 4 is an illustration of the vehicle 10 towing a trailer 50 around a curve 52 in a road 54. In this embodiment, the vehicle 10 is equipped with a hitch angle sensor 56 that measures the hitch angle between the hitch post on the vehicle 10 and the hitch post on the trailer 50 to provide rear viewing angle correction. Because the trailer 50 blocks some of the rear viewing of the rear-view mirrors 16 and 18, the present invention proposes automatically changing the viewing angle of the rear-view mirrors 16 and 18 a proper amount based on the degree of curvature of the curve 52 and the dimensions of the trailer 50 to provide a corrected rear viewing zone 58 were a vehicle 48 will be visible to the driver of the vehicle 10. As will be discussed below, the corrected rear viewing zone 58 is turned out farther than the corrected rear viewing zone 26 when the curvature of the curves 12 and 52 is the same.

FIG. 5 is a block diagram of a mirror angle adjustment system 60, according to an embodiment of the present invention. Box 62 is intended to represent one or more devices and/or sensors that are on the vehicle 10 that will provide vehicle parameters and/or road curvature information so that the system 50 can calculate the proper amount that the rear-view mirrors 16 and 18 need to be adjusted to provide the optimum rear viewing angle. These sensors and devices can include one or more of a camera, a GPS receiver, a digital map, a vehicle speed sensor, a vehicle steering angle sensor, a yaw-rate sensor, a hitch angle sensor, etc. It will be readily apparent to any person with ordinary skill in the art that other parameters than those suggested can be used to determine the curvature of the road.

The various parameters from the box 62 are sent to a road curvature estimation processor 64 that calculates the curvature of the road based on the input signals and associated algorithms, as will be discussed in detail below. In this context, road curvature also refers to an uphill and downhill slope of the road. The road curvature information from the processor 64 is then sent to a direction determination processor 66 that determines which way the road is curving, either up, down, left, right, up and to the left, up and to the right, down and to the left and down and to the right. For those road curvatures only to the right, only the right side rear-view mirror 18 is adjusted. For those road curvatures only to the left, only the left side rear-view mirror 16 is adjusted. For those road curvatures up or down, both of the rear-view mirrors 16 and 18 are adjusted.

Depending on the direction determination by the direction determination processor 66, the road curvature information is sent to a left mirror angle adjustment calculation processor 68 and/or a right mirror angle adjustment calculation processor 70 to determine the proper adjustment to the side rear-view mirrors 16 and/or 18. Depending on the calculated adjustment angle for the left side rear-view mirror 16 from the processor 68, a left side motor 72 will adjust the mirror 16 at box 74. Likewise, depending on the calculated adjustment angle for the right side rear-view mirror 18 from the calculation processor 70, a right side motor 76 will adjust the mirror 18 at box 78.

According to one embodiment of the present invention, the only information that is available from the box 62 to determine the curvature ρ of the road is vehicle speed and steering angle. There may be various reasons why the vehicle does not have other information that can be used to determine road curvature, such as the GPS receiver is out, the vehicle is not equipped with a GPS receiver, the vehicle is not equipped with digital maps, the yaw-rate sensor has failed, etc.

FIG. 6 is an illustration of the vehicle 10 traveling around a curve 80 in a road 82, where line 84 represents the turning radius R of the vehicle 10. Using equation (1) below, the curvature ρ of the curve 80 can be calculated with just the vehicle speed v and the vehicle steering angle along with other known and fixed parameters. The road curvature ρ is equal to the reciprocal of the turning radius R as 1/R. From the road curvature ρ, the corrected viewing angle Δα of the rear-view mirrors 16 or 18 can be calculated.

$\begin{matrix} {\rho = {\frac{\frac{1}{L}}{1 + \frac{K_{us}v^{2}}{Lg}}\left( {\delta_{f} - \delta_{r}} \right)}} & (1) \end{matrix}$ Where L is the wheel base of the vehicle 10, K_(us) is a coefficient, v is the vehicle speed, g is acceleration due to gravity, δ_(F) is the front wheel steering angle and δ_(R) is the rear steering angle.

FIG. 7 is an illustration of the vehicle 10 traveling around a curve 90. The normal rear viewing zone 22 of the right side rear-view mirror 18 is defined by an original line of sight 92 and the corrected rear viewing zone 26 of the mirror 18 is defined by a corrected line of sight 94, where the corrected viewing angle Δα is the angle between the lines 92 and 94. The radius of curvature ρ is identified by line 96 and a value e is defined as the distance between the edge of the curve 90 and a line 100 that is a side line of the vehicle 10. Line 98 represents the distance between the point of origin and the corrected line of sight 94, and is defined as R−e. The angle between the lines 96 and 98 and the angle between the line 100 and the corrected line of sight 94 are the same and are defined as α. The angle α₀ is an original angle between the line 100 and the line 92. Further, the curvature value ρ₀ and Δρ are intermediate variables. The actual mirror correction value θ provided by the motors 72 and 76 is θ=Δα/2. Based on the following equations, the corrected viewing angle Δα can be determined as follows.

$\begin{matrix} {{\cos(\alpha)} = {\frac{R - e}{R} = {1 - {ep}}}} & (2) \\ {\alpha = {{\alpha_{o} + {\Delta\;\alpha\mspace{31mu}\rho}} = {\rho_{o} + {\Delta\;\rho}}}} & (3) \\ {\rho_{o} = \frac{1 - {\cos\left( \alpha_{o} \right)}}{e}} & (4) \\ {{\Delta\;\alpha} = {\left( \frac{\mathbb{d}\alpha}{\mathbb{d}\rho} \right)\Delta\;\rho}} & (5) \\ {\frac{\mathbb{d}\alpha}{\mathbb{d}\rho} = {\frac{e}{\sin(\alpha)} = \frac{e}{\sqrt{e\;{\rho\left( {2 - {e\;\rho}} \right)}}}}} & (6) \\ {{\Delta\;\alpha} = {{\alpha - \alpha_{o}} = {\frac{e}{\sqrt{e\;{\rho\left( {2 - {e\;\rho}} \right)}}}\left( {\rho - \rho_{o}} \right)}}} & (7) \end{matrix}$

FIG. 8 is an illustration of the vehicle 10 traveling over a hill 110, where the viewing angle of the mirrors 16 and 18 will be turned down to provide the optimum rear viewing zone based on the slope of road. An original line of sight 112 is defined for the normal rear viewing zone 22 and a corrected line of sight 114 is defined for the corrected rear viewing zone 36. The corrected viewing angle Δα between the lines 112 and 114 is determined in the same manner as discussed above for FIG. 7, where line 116 represents the line 96 and line 118 represents the line 98. In this embodiment, the value e is the height of the mirror 16 or 18 above the ground. Therefore, equations (2)-(7) can be used in the same manner to determine the corrected viewing angle Δα.

In the embodiment for determining the corrected viewing angle Δα when the vehicle 10 is traveling uphill or downhill, the curvature ρ of the hill 110 cannot be determined by the vehicle speed and the steering angle. Therefore, the road curvature ρ needs to be determined by other methods at the box 64, such as GPS receiver, maps, etc.

FIG. 9 is an illustration of the vehicle 10 pulling the trailer 50 around a curve 120. In this embodiment, the sensors and other devices at the box 62 would also include the hitch angle sensor, and the left mirror angle adjustment calculation processor 68 and the right mirror angle adjustment calculation processor 70 would calculate the corrected viewing angle of the rear-view mirrors 16 and 18, respectively, as discussed below. Because the vehicle 10 is towing the trailer 50, the corrected viewing angle Δα will need to be greater than if the vehicle 10 was not towing the trailer 50 for the same radius of curvature ρ of the road. The corrected rear viewing zone 58 of the mirror 18 is defined by a corrected line of sight 122. In this calculation for the corrected viewing angle Δα, the hitch angle η from the hitch angle sensor 56 is used. If the length and the width of the trailer 50 are not known, then the corrected viewing angle Δα is set to be equal to the hitch angle η. However, if the width and the length of the trailer 50 are known, then a more accurate corrected viewing angle Δα can be obtained.

FIG. 10 is another illustration of the vehicle 10 towing the trailer 50, where the trailer 50 is shown in a straight orientation when the vehicle 10 is traveling straight and is shown in an angled orientation when the vehicle 10 is traveling around a curve. FIG. 10 is provided to show a triangle 130 where the trailer 50 is straight between the right side rear-view mirror 18, the front-center of the trailer 50 and the rear right corner of the trailer 50. A triangle 132 is also shown for the same points when the trailer 50 is in the angled configuration. The triangle 130 includes the angles φ and ζ and the side dimensions W, L and D. Likewise, the triangle 132 includes the angles φ′ and ζ′ and the side dimensions W′, L′ and D′. Because the dimensions of the trailer 50 are known, the variables W, L, D, φ and ζ are also known. From these values, the following equations can be used to calculate the corrected viewing angle Δα based on the angle of the trailer 50.

$\begin{matrix} {{W = W^{\prime}},{D = D^{\prime}}} & (8) \\ {\varphi^{\prime} = {\varphi - \eta}} & (9) \\ {L^{\prime\; 2} = {D^{\prime\; 2} + W^{\prime\; 2} - {2\; D^{\prime}W^{\prime}\cos\;\varphi^{\prime}}}} & (10) \\ {\zeta^{\prime} = {\sin^{- 1}\left( {\frac{D^{\prime}}{L^{\prime}}\sin\;\varphi^{\prime}} \right)}} & (11) \\ {{\Delta\;\alpha_{trailer}} = {\zeta^{\prime} - \zeta}} & (12) \end{matrix}$

The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims. 

1. A method for correcting a viewing angle of a rear-view mirror on a vehicle when the vehicle is traveling around a curve, said method comprising: determining the curvature of the road using only a speed of the vehicle and a steering angle of the vehicle; calculating a corrected mirror viewing angle based on the curvature of the road; and changing the viewing angle of the rear-view mirror using the corrected viewing angle.
 2. The method according to claim 1 wherein determining the curvature of the road includes using the equation: $\rho = {\frac{\frac{1}{L}}{1 + \frac{K_{us}v^{2}}{Lg}}\left( {\delta_{f} - \delta_{r}} \right)}$ where ρ is the curvature of the road, L is the wheel base of the vehicle, K_(us) a coefficient, v is the vehicle speed, g is acceleration due to gravity, δ_(F) is the front wheel steering angle and δ_(R) is the rear steering angle of the vehicle.
 3. The method according to claim 1 wherein calculating a corrected mirror viewing angle includes calculating the angle using the curvature of the road and the radius of the curve.
 4. The method according to claim 3 wherein the corrected viewing angle is calculated by the equation: ${\Delta\;\alpha} = {{\alpha - \alpha_{o}} = {\frac{e}{\sqrt{e\;{\rho\left( {2 - {e\;\rho}} \right)}}}\left( {\rho - \rho_{o}} \right)}}$ where Δα is the corrected mirror angle, e is the distance between an edge of the curve and a side line of the vehicle, α is the angle between the center of the lane and the corrected viewing line, α₀ is the angle between the side line and an original viewing angle line of the rear-view mirror and ρ is the curvature.
 5. The method according to claim 1 wherein only the rear-view mirror that is on the side of the vehicle towards the direction that the road is curving will be corrected.
 6. The method according to claim 1 wherein determining the curvature of the road using only a speed of the vehicle and a steering angle of the vehicle includes determining the speed of the vehicle and the steering angle of the vehicle using vehicle sensors.
 7. The method according to claim 1 wherein determining the curvature of the road using only a speed of the vehicle and a steering angle of the vehicle includes determining the steering angle of both front wheels and rear wheels of the vehicle.
 8. A method for correcting a viewing angle of a rear-view mirror on a vehicle when the vehicle is traveling around a curve, said method comprising: determining the curvature of the road using only a speed of the vehicle and a steering angle of the vehicle by the equation: $\rho = {\frac{\frac{1}{L}}{1 + \frac{K_{us}v^{2}}{Lg}}\left( {\delta_{f} - \delta_{r}} \right)}$ where ρ is the curvature of the road, L is the wheel base of the vehicle, K_(us) is a coefficient, v is the vehicle speed, g is acceleration due to gravity, δ_(F) is the front wheel steering angle and δ_(R) is the rear steering angle of the vehicle; calculating a corrected mirror viewing angle based on the curvature of the road including calculating the angle using the curvature of the road and the radius of the curve; determining whether a left side rear-view mirror or a right side rear-mirror should be changed; and changing the viewing angle of the mirror using the corrected viewing angle.
 9. The method according to claim 8 wherein the corrected viewing angle is calculated by the equation: ${\Delta\;\alpha} = {{\alpha - \alpha_{o}} = {\frac{e}{\sqrt{e\;{\rho\left( {2 - {e\;\rho}} \right)}}}\left( {\rho - \rho_{o}} \right)}}$ where Δα is the corrected mirror angle, e is the distance between an edge of the curve and a side line of the vehicle, α is the angle between the center of the lane and the corrected viewing line, α₀ is the angle between the side line and an original viewing angle line of the rear-view mirror and ρ is the curvature.
 10. The method according to claim 8 wherein only the rear-view mirror that is on the side of the vehicle towards the direction that the road is curving will be corrected.
 11. The method according to claim 8 wherein determining the curvature of the road using only a speed of the vehicle and a steering angle of the vehicle includes determining the speed of the vehicle and the steering angle of the vehicle using vehicle sensors.
 12. The method according to claim 8 wherein determining the curvature of the road using only a speed of the vehicle and a steering angle of the vehicle includes determining the steering angle of both front wheels and rear wheels of the vehicle.
 13. A system for correcting a viewing angle of a rear-view mirror on a vehicle when the vehicle is traveling around a curve, said system comprising: means for determining the curvature of the road using only a speed of the vehicle and a steering angle of the vehicle; means for calculating a corrected mirror viewing angle based on the curvature of the road; and means for changing the viewing angle of the mirror using the corrected viewing angle.
 14. The system according to claim 13 wherein the means for determining the curvature of the road includes using the equation: $\rho = {\frac{\frac{1}{L}}{1 + \frac{K_{us}v^{2}}{Lg}}\left( {\delta_{f} - \delta_{r}} \right)}$ where ρ is the curvature of the road, L is the wheel base of the vehicle, K_(us) is a coefficient, v is the vehicle speed, g is acceleration due to gravity, δ_(F) is the front wheel steering angle and δ_(R) is the rear steering angle of the vehicle.
 15. The system according to claim 13 wherein the means for calculating a corrected mirror viewing angle calculates the angle using the curvature of the road and the radius of the curve.
 16. The system according to claim 13 wherein the means changing the viewing angle corrects the viewing angle uses the equation: ${\Delta\alpha} = {{\alpha - \alpha_{o}} = {\frac{e}{\sqrt{e\;{\rho\left( {2 - {e\;\rho}} \right)}}}\left( {\rho - \rho_{o}} \right)}}$ where Δα is the corrected mirror angle, e is the distance between an edge of the curve and a side line of the vehicle, α is the angle between the center of the lane and the corrected viewing line, α₀ is the angle between the side line and an original viewing angle line of the rear-view mirror and ρ is the curvature.
 17. The system according to claim 13 wherein only the rear-view mirror that is on the side of the vehicle towards the direction that the road is curving will be corrected.
 18. The system according to claim 17 wherein the means for determining the curvature of the road using only a speed of the vehicle and a steering angle of the vehicle determines the speed of the vehicle and the steering angle of the vehicle using vehicle sensors.
 19. The system according to claim 13 wherein the means for determining the curvature of the road using only a speed of the vehicle and a steering angle of the vehicle determines the steering angle of both front wheels and rear wheels of the vehicle. 